docs(packaging): document desktop GUI frontends and optdepends

The GUI frontends landed with README/CLI/operations docs but no packaging
coverage. Add a PACKAGING.md section with the command/script/requirement
table for both frontends, note why stdlib tkinter is still an optdepend
rather than a hard dependency, and record that packaging must not grant the
GUIs privileges beyond the operator's own account.

Add the matching PKGBUILD optdepends (`tk`, `pyside6`), plus
`python-pystray`/`python-pillow` for the tray applet, which were never
listed when it shipped. Also add `gui/` to the CLAUDE.md architecture notes
and state snapshot.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JX86xeoBJVBb16qHkDf53K

CLAUDE.md

@@ -87,6 +87,10 @@ Implemented investigation/response state:
   runs `check --json` quick checks. Its logic modules (`tray/state.py`,
   `actions.py`, `notify.py`) are GUI-free and tested; only `tray/app.py`
   imports GUI libs, and the core agent stays stdlib-only.
+- Optional windowed desktop dashboards mirror the same pattern:
+  `enodia-sentinel gui` (stdlib tkinter) and `enodia-sentinel gui-qt`
+  (`[qt]` extra with PySide6). Both are read-only over detection state, share
+  the GUI-free `gui/model.py`, and display response plans for review only.
 - IPS behavior is currently explicit workflow: posture hardening plus reviewed
   dry-run containment actions. There is no automatic inline blocking or silent
   host mutation yet.
@@ -156,6 +160,10 @@ Start with:
 - `tray/` is the optional desktop tray frontend over the CLI and systemctl;
   only `tray/app.py` may import `pystray`/`PIL` (enforced by an import-guard
   test).
+- `gui/` is the optional windowed desktop dashboard. `gui/model.py` is the
+  GUI-free presentation model over `tui.collect_model`; only `gui/app.py`
+  (tkinter) and `gui/qt_app.py` (PySide6, `[qt]` extra) import GUI libraries,
+  enforced by import-guard tests.
 - `go-agent/` is the isolated Phase 1 sidecar with Go config, process-state,
   detector, schema, and sweep-loop packages. It writes JSONL to stdout and
   must not share or mutate Python daemon state during parity development.